This invention relates to a form for concealing variable information printed on the form by a printer, e.g. laser, ink jet or impact printer.
It is known from International Patent Application PCT/US97/02149 published Sep. 4, 1997 to, during manufacture of a valuable document such as a check or the like, (a) print a background scrambling pattern on the valuable document and (b) overprint or xe2x80x9ctrap producexe2x80x9d a static message (e.g. xe2x80x9cSTOPxe2x80x9d) in thermochromatic ink such that the static message is initially invisible due to the presence of the background scrambling pattern.
Radiant heat generated during photocopying or scanning of the valuable document causes the previously invisible static message (e.g. xe2x80x9cSTOPxe2x80x9d) to become visible (e.g. by changing color) such that it is readily apparent that the original valuable document has been copied. Likewise, the static message is visible in any copies of the valuable document.
Thus, this prior art document teaches a device for indicating when a valuable document has been copied by a photocopier or scanner.
The present invention involves the use of a background scrambling pattern printed during manufacture on a form and upon which, at a time after manufacture, variable confidential information can be printed by a printer such as a laser, ink jet or impact printer. When printed over the background scrambling pattern, the variable confidential information immediately and automatically cannot be read due to the presence of the background scrambling pattern which prevents the observer""s eye from discriminating the overlying variable confidential information from the underlying background scrambling pattern.
In order to assist in hiding the confidential information, such information may be printed in a light color or in a light screen density. Additionally, the entire scrambling pattern can be printed with a very light screen so that the confidential message is further hidden among the background screen.
The background scrambling pattern is formed from a thermochromatic ink and the optical characteristics of the background scrambling pattern alter upon the application of heat, such as, for example, the heat generated by a person physical rubbing the form with their fingers. The alteration in the optical characteristics of the background scrambling pattern then allows the variable confidential information to be discriminated from the altered background scrambling pattern.
Desirably, the thermochromatic ink remains irreversibly in its altered state after the heat is removed so that a later observer can determine whether the information has been previously read by a third party. Such an embodiment is tamper-evident. In such an embodiment, a printer must be used that does not generate significant heat, such as a cold laser, ink jet or impact printer.
In another embodiment, the thermochromatic ink may return to its original state, it which case the embodiment is, of course, not tamper-evident. In this case, either a cold or hot printer system could be used to print the confidential information on the form.